Fix Dockerfile parser (#459)

Co-authored-by: CrazyMax <crazy-max@users.noreply.github.com>

pkg/dockerfile/client_test.go

@@ -0,0 +1,74 @@
+package dockerfile_test
+
+import (
+	"fmt"
+	"os"
+	"testing"
+
+	"github.com/crazy-max/diun/v4/pkg/dockerfile"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+var (
+	dc *dockerfile.Client
+)
+
+func TestMain(m *testing.M) {
+	var err error
+
+	dc, err = dockerfile.New(dockerfile.Options{
+		Filename: "./fixtures/valid.Dockerfile",
+	})
+	if err != nil {
+		panic(err.Error())
+	}
+
+	os.Exit(m.Run())
+}
+
+func TestNew(t *testing.T) {
+	assert.NotNil(t, dc)
+}
+
+func TestLoadFile(t *testing.T) {
+	cases := []struct {
+		name    string
+		dfile   string
+		wantErr bool
+	}{
+		{
+			name:    "Failed on non-existing file",
+			dfile:   "",
+			wantErr: true,
+		},
+		{
+			name:    "Fail on empty file",
+			dfile:   "./fixtures/empty.Dockerfile",
+			wantErr: true,
+		},
+		{
+			name:    "Fail on wrong file format",
+			dfile:   "./fixtures/invalid.Dockerfile",
+			wantErr: true,
+		},
+		{
+			name:    "Valid",
+			dfile:   "./fixtures/valid.Dockerfile",
+			wantErr: false,
+		},
+	}
+	for _, tt := range cases {
+		t.Run(tt.name, func(t *testing.T) {
+			c, err := dockerfile.New(dockerfile.Options{
+				Filename: tt.dfile,
+			})
+			if tt.wantErr {
+				fmt.Println(err)
+				require.Error(t, err)
+				return
+			}
+			assert.NotNil(t, c)
+		})
+	}
+}